The investigation which led to this invention was directed particularly toward stabilizing a powdered diphenylamine antioxidant (mixture of styrenated diphenylamines obtained as Wingstay 29, a trademark of Goodyear Tire & Rubber Company) absorbed onto a hydrous calcium silicate obtained as Micro-Cel E, a product of Johns-Manville Co. The Micro-Cel E has nominal properties as follows: specific gravity of 2.45, bulk density of 5.5 pounds per cubic foot (8.79 Kg/m.sup.3), and an ability of absorb 490 percent of its weight in oil.
The generic formula of the diphenylamines to which this invention is applicable is: ##STR1## wherein R and R.sub.1 are selected from hydrogen (provided only one of them is hydrogen) tertiary alkyl radicals having 4 to 12 carbon atoms (4-12C) and the group ##STR2## wherein R.sub.3 is selected from H and methyl and R.sub.4 is selected from phenyl and p-tolyl radicals; and R.sub.2 is selected from H and 1-methyl benzyl.
Wingstay 29 powder is normally sold in a ratio of about 68 weight percent Wingstay 29 to 32 weight percent Micro-Cel E and is normally a light tan color. One of its uses is in compounds for rubber bands.
A variety of organic and inorganic chemicals were tested as additives to halt the color formation. Neither tris (nonylphenyl) phosphite nor sodium borohydride prevented discoloration. Dilauryl thiodipropionate had a slight benefit.